1. Field of the Invention
The present invention relates to the microelectromechanical system (MEMS) field, and more particularly to a transverse acoustic wave resonator, an oscillator having the resonator and a method for fabricating the resonator.
2. Description of Related Art
Oscillators are electronic components widely used in electrical industries for generating repetitive electrical signals, usually sine waves or square waves. According to different working theories, the oscillators are divided into resistance-capacitance (RC) oscillators, inductance-capacitance (LC) oscillators, quartz crystal oscillators (XOs) and recent MEMS oscillators.
In a long former time, due to excellent stabilities of temperature and frequency and high quality factors, conventional quartz crystal oscillators are applied in almost all electronic products including consumer products, industrial controlling products and military products etc. However, after entering into mobile multimedia times, handset devices bring out the higher demands about the components regarding their energies, profiles and costs. Comparing with the conventional quartz crystal oscillators, the MEMS oscillators, because of their advantages of lower profiles, higher integration rates with CMOS and lower costs, wider and adjustable frequency ranges, are getting more and more preferred in consumer electronics and communication products. American Discera Corporation and Sitime Corporation respectively invent active MEMS oscillators and release related products applied in various kinds of consumer electronics.
An MEMS oscillator usually includes an MEMS resonator, an energizing circuit and a frequency compensation circuit. According to their different capabilities and applied areas, the MEMS oscillators are divided into normal oscillators, voltage-controlled oscillators (VCOs), temperature-controlled oscillators and constant-temperature oscillators etc. According to their different structures of intrinsic capacitive-type resonators, the MEMS oscillators are divided into comb oscillators, clamped beam oscillators, disk oscillators and ring oscillators etc. Besides, according to their different working theories, the MEMS oscillators are divided into surface acoustic wave (SAW) oscillators and bulk wave oscillators among which the bulk wave oscillators, because of their higher quality factors and lower resonance impedance comparing with the SAW oscillators, are becoming the main developing trend in recent research and realizable products.
Hence, it is desirable to provide an improved transverse acoustic wave resonator, an oscillator having the resonator and a method for fabricating the resonator.